424 



Fishery Bulletin 94(3). 1996 



A rochet 



Figure 1 



Auxis thazard (top) and A. rochei (bottom) showing anterior extent of dorsal scaleless area in 

 relation to distal end of pectoral fin (left line) and width of corselet under origin of second dorsal 

 fin (right line). 



Roa, 1991). Richards (1984:28) concluded that Auxis 

 ". . . is the most widely distributed and abundant 

 scombrid in tropical seas." With stocks of other tuna 

 species continually diminishing, there is increased 

 potential for greater exploitation of Auxis. Before 

 exploitation increases, it is necessary to establish how 

 many species exist and what their correct names are, 

 to determine how to identify them, and to obtain some 

 idea of the major worldwide populations. 



Fitch and Roedel ( 1963) also showed that the east- 

 ern Pacific populations of both species differed sig- 

 nificantly from the Indo-West Pacific populations but 

 did not name them pending further work. We con- 

 firm Fitch and Roedel's findings that the eastern 

 Pacific population of A. thazard has more gill rakers 

 (usually 43—48) than other populations (usually 38- 

 42 in Atlantic and Indo-West Pacific populations), 

 similar to the counts for A. rochei. The eastern Pa- 

 cific population of A. rochei has an even wider corse- 

 let (usually more than 20 scales wide under the sec- 

 ond dorsal fin) than other populations (8-19 scales 

 in populations from the Indo-West Pacific). 



This paper distinguishes the two species. We have 

 located the type specimen of rochei and designate a 

 neotype for thazard to stabilize current use of these 



names for these species. We evaluate the systematic 

 status of eastern Pacific populations of the two spe- 

 cies and describe them as new subspecies, Auxis 

 thazard brachydorax and Auxis rochei eudorax. 



Materials and methods 



Methods follow those used by Collette and Gillis 

 (1992), in a revision of the double-lined mackerels 

 Grammatorcynus, and by Collette and Russo ( 1985) 

 in a revision of the Spanish mackerels Scomber- 

 omorus. Morphometric characters used in this study 

 are as follows: FL (fork length); HdL (head length); 

 P1L (pectoral-fin length); PIT (distance from pecto- 

 ral-fin tip to anterior edge of dorsal scaleless area 

 above lateral line); and CW (corselet width under 

 second dorsal-fin origin). Owing to the different 

 shapes of A. rochei and A. thazard, we postulated 

 that four body depth measurements would illustrate 

 these differences: IDor (body depth at origin of first 

 dorsal); IDend (body depth at posterior end of first 

 dorsal); 2Dor (body depth at origin of second dorsal); 

 and Aor (body depth at anal-fin origin). Auxis rochei 

 is a more slender species and the four body depth 



